1. Field of the Invention
This invention relates to a new polyester composition comprising linear polymers produced by condensation reactions of polymethylene glycols and dicarboxylic acids or their esters, and more particularly to such polyester compositions containing a hydantoin derivative that exhibit improved dyeability, thermal oxidative stability, light stability and dyed light fastness, compared to other polyalkoxy-modified polyesters.
2. Description of the Prior Art
It is well known that the polymeric polyesters prepared by polycondensation of a dihydric alcohol or its functional derivatives and a dicarboxylic acid or a polyester-forming derivative thereof, such as an acid halide, or a simple ester of a dibasic acid and a volatile monohydric alcohol are excellent fiber-forming polymers. Commercially the most important polyesters are those prepared by the condensation of terephthalic acid or dimethyl terephthalate and a polymethylene glycol containing from two to ten carbon atoms, and particularly ethylene glycol. These polyesters are relatively inert hydrophobic materials capable of being formed into filaments which can be drawn to produce textile fibers of superior strength and pliability. However, since these materials are not readily permeable to water, they cannot be satisfactorily dyed by the ordinary dyeing procedures such as used in dyeing cotton, wool, natural silk and regenerated cellulose.
Further limitations in the development of polyethylene terephthalate fibers for cloths, include the problem of pilling and the hard touch of clothing. The compact molecular structure of polyethylene terephthalate fibers makes it quite difficult, except with a limited number of dyes, to obtain a high degree of dyebath exhaustion or to secure satisfactory deep shades. Absorption and penetration of the dye into the fiber core are limited by the inherent properties of the fiber. A number of methods have been proposed to increase the dyeability of polyesters; however, most have not proved to be entirely satisfactory. One such method is to copolymerize a third component in addition to terephthalic acid and ethylene glycol as the main components to eliminate or minimize the limitations of polyethylene terephthalate fibers, and especially improve the ease of dyeing. Generally, the amount of the third component is kept small, with the intention of improving a certain portion of the physical properties and keeping the other properties of the polyethylene terephthalate fiber unchanged.
For example, in U.S. Pat. No. 2,905,657 the dyeability of polyethylene terephthalate has been improved by the addition of a third component that functions as a chain-terminating agent. By adding a minor proportion of monohydroxy compounds to polyethylene terephthalate polymers the polymers are more readily dyeable to deeper and more uniform colors than the unmodified polyethylene terephthalate. It has been found, however, that although the dye affinity of the polyester has been increased, other desirable properties of the filament produced from the polyester have been sacrificed. Employing chain terminating monohydroxy compounds in the polymer molecule causes a reduction in the molecular weight of the polyester as evidenced by a reduction in its viscosity. To overcome this disadvantage while still retaining the benefit of the dye affinity exhibited by the chain terminating compounds U.S. Pat. No. 2,895,946 discloses the incorporation of a small amount of a chain-branching agent in the polyester reaction mixture, along with a chain terminating agent, so that a polyester can be produced which not only possesses the desired dye affinity but also has the necessary molecular weight. However, it has been found that this modified polyester cannot be melt spun into a textile fiber at the same rate as the unmodified polyethylene terephthalate fiber. The increased production cost therefore offsets in a large measure the advantage of improved dyeability provided by the modifying additives.
Another approach to improving the dyeability of polyethylene terephthalate fibers is disclosed in U.S. Pat. No. 2,744,087. In this patent a third component is added to provide a more readily dyeable copolyester. This component is polyethylene glycol and provides an improvement over unmodified polyethylene terephthalate with respect to dyeability. It has been found that this product suffers from thermal instability; and accordingly, its practical application has been severely restricted.
The dyeability of polyethylene terephthalate fibers can also be improved by using carriers or pressurized and high temperature dyeing equipment. Carriers or accelerants, however, increase dyeing costs and frequently impair quality by spotty or non-uniform dyeing. Likewise, the use of high temperature dyeing increases fabric cost because of the expensive specialized equipment involved in such dyeing.
An extremely desirable property that enhances the utility of polyesters is thermal stability. This is an important property because many processes for polyesters fibers and fabrics involve exposure to heat in air for varying periods of time. Such heating is usually employed in dyeing the fibers, heat setting the fibers for enhanced dimensional stability and in texturing the fibers to improve recovery characteristics of woven fabrics. Processing polyester filaments, staple, blends, fabrics and the like may require subjecting the polyester product to temperatures up to 230.degree. C. For satisfactory performance of these fibers and fabrics in various end uses, stability of the polymer to these processing conditions therefore is an essential requirement.
Ordinarily, in the commercial manufacture of polyester filaments, fiber and the like, the filaments may be subjected to a heat-set treatment at temperatures in the 100.degree.-200.degree. C. range subsequent to the orientation drawing of the filament, but prior to end use processing. For example, heat setting of crimped polyester filaments prior to being cut into staple is often accomplished in the 100.degree. to 150.degree. C. temperature range and heat setting dyed and undyed fabrics to achieve dimensional stability is typically in the 150.degree.-200.degree. C. temperature range.
It is therefore an object of this invention to provide polyesters having increased dyeability, thermal oxidative stability, light stability and dyed light fastness and a process for producing such polyesters.